Does the size of subsamples taken from multispecies trawl catches affect estimates of catch composition and abundance?

Although subsampling is a common method for describing the composition of large and diverse trawl catches, the accuracy of these techniques is often unknown. We determined the sampling errors generated from estimating the percentage of the total number of species recorded in catches, as well as the abundance of each species, at each increase in the proportion of the sorted catch. We completely partitioned twenty prawn trawl catches from tropical northern Australia into subsamples of about 10 kg each. All subsamples were then sorted, and species numbers recorded. Catch weights ranged from 71 to 445 kg, and the number of fish species in trawls ranged from 60 to 138, and invertebrate species from 18 to 63. Almost 70% of the species recorded in catches were “rare” in subsamples (less than one individual per 10 kg subsample or less than one in every 389 individuals). A matrix was used to show the increase in the total number of species that were recorded in each catch as the percentage of the sorted catch increased. Simulation modelling showed that sorting small subsamples (about 10% of catch weights) identified about 50% of the total number of species caught in a trawl. Larger subsamples (50% of catch weight on average) identified about 80% of the total species caught in a trawl. The accuracy of estimating the abundance of each species also increased with increasing subsample size. For the “rare” species, sampling error was around 80% after sorting 10% of catch weight and was just less than 50% after 40% of catch weight had been sorted. For the “abundant” species (five or more individuals per 10 kg subsample or five or more in every 389 individuals), sampling error was around 25% after sorting 10% of catch weight, but was reduced to around 10% after 40% of catch weight had been sorted.

Preliminary observations on the nursery management of post larvae of Penaeus monodon

Post larvae of tiger prawn (Penaeus monodon) of the size 10-12 mm were stocked at the rate of 10 lakhs/ha in a manured cement nursary pond which was initially fertilized with chemical manures. Water exchange was attended once in a week. Artificial feeding was given in the form of minced clam meat. After a month, the pond was harvested. The juveniles which have grown to 40-46 mm size were recovered. The percentage of survival from post larvae to juveniles was 85.45%.

Recent advances and scope for sea farming in India

Although brackishwater prawn and fish culture was traditionally practiced for a long time in the country, efforts at sea farming are still in their infancy. During the past 15 years the Central Marine Fisheries Research Institute has developed various technologies for sea farming of mussels, pearl oysters, production of cultured pearls, edible oysters, clams, prawns, lobsters, seaweeds and more recently sea cucumbers and top shells. The paper outlines recent developments in these areas as well as in others like sea ranching of marine prawns and pearl oyster, and scope for enlarging sea farming activities including development of artificial reefs in India.

Influence of salinity on population growth of a rotifer, Brachionus plicatilis (Mullen)

The rotifer Brachionus plicatilis plays an important role in prawn hatcheries. It tolerates a wide range of salinities. The present experiments were conducted to find the optimum salinity for its mass culture. Experiments conducted on various ranges of salinities starting from 0 to 40 ppt at an interval of 5 ppt revealed that Brachionus plicatilis did not survive at salinities 0 and 40 ppt. Optimum salinity studies conducted at 5-15 ppt with an interval of 1 ppt showed that the production of 70 individuals/ml was highest at 10 ppt salinity and the doubling time ranged from 1.728 to 1.317 days.

Culture of Moina micrura on various organic waste products

Moina micrura, a cladoceran species, is considered to be one of the best live food organisms for rearing the young larval stages of fish and prawn. Considering the importance of this species in hatchery operations the present study was undertaken to record its fecundity and life span and to culture it using different locally available organic waste products. In indoor culture, a maximum production of 2600 ind/1 and a minimum of 1050 ind/1 were obtained when treated with gram + maize oilcake and "till" oilcake respectively. In outdoor culture, a highest production of 6000 ind/1 was achieved with "Alsi" and "till" oilcakes and a lowest density of 1050 ind/1 with coconut oilcake and raw cattle dung was obtained with an inoculation rate of 5 ind/1.

Effect of dietary protein level on the growth of Deccan mahseer fry Tor khudree Sykes

Four feeds having different protein levels were separately tested on Tor khudree fry having an average length of 23.5 mm and weight 55 mg. The best average growth of 15.66 mg and 0.456 mm/day was obtained with Feed IV which comprised rice bran, ground nut oil cake, Acetes, wheat flour and mineral mix at the ratio of 1:1:1:0.7143:0.01428. These constitute 35.29% of proteins. The Feed II which comprised R.B + G.O.C. + prawn shell + wheat flour and mineral mix at a ratio of 1:1:1:0.7143:0.01428 contained 32.61% crude proteins. It provided a growth rate of 14.83 mg and 0.440 mm per day. The conversion rates were 38.258 and 37.776 for feeds IV and II respectively. Since Feed II is cheaper than Feed IV and provides almost equal growth rate, it can be used in the nurseries for intensive rearing of T. khudree fry.

Role of microalgae in conditioning water in penaeid larval culture

Microalgae play an important role in conditioning water quality for penaeid larval culture. Recently it has been demonstrated that a modification of the green water larval culture system (Ling, 1969) for Macrobrachium allows the production of post larvae without any water change, despite extensive use of artificial feeds (Ang and Cheah, 1986). Increase of toxic metabolites such as ammonia and nitride are also common in penaeid larval culture, especially where excessive amounts of artifial feeds are employed. Present work examines the use of six marine microalgae at four cell concentrations as a "biological filter" system, to control and detoxify levels of ammonia and nitrite in P. monodon larval culture water whilst using artificial diet. Preliminary results indicate that amongst the six algal species tested, C. japonica at 1000 cell μlˉ¹ was most effective in reducing accumulated toxic metabolites from an unchanged culture water environment.

Deepwater prawns and lobsters off the Kerala coast

Majority of the prawn catch of the Kerala coast comes from the inshore regions within the 10 fathom line. A bottom deposit formed of fine mud rich in humus is found to be the ideal condition for the penaeid prawns. Similarly the lobster is observed in large numbers at localised areas very near the coast in the crevices of rocks. Though it has been observed that prawns and lobsters exist in deep water as well under different conditions, our knowledge about these forms along the Indian coasts is very scanty, being restricted to the works of Spence Bate, Alcock, De Man and Ramadan. Recently, during the cruises of the University Research Vessel Conch off the Kerala Coast (1958-1963) two species of deep water prawns and one species of lobster were collected from depths 100 - 180 fathoms. Of these, Penaeopsis philippi is found in large numbers occupying an almost continuous bed extending from Anjengo to Mangalore, while P. rectacutus has a restricted appearance between Cochin and Calicut. However, some sort of year to year variation has also been observed regarding the abundance of the species at various stations. Peurulus sewelli has a more restricted distribution, the maximum number being found between Puvar and Cochin. Attempt has been made to correlate the occurrence of the species with the hydrological conditions at the bottom and the nature of the substratum. It is observed that Peurulus sewelli occupies a more or less hard bed formed of sand with shell fragments or stones and small percentage of silt, the bottom temperature at the stations varying from 11°C to l4°C. P. sewelli is a more or less permanent inhabitant of the edge of the continental shell off the Kerala Coast worthy of attention for detailed investigation with a view to explore the possibilities of commercial exploitation.

Note on the size groups of prawns landed by shrimp trawls of four different cod end meshes

A study on the different size groups of prawns caught by four shrimp trawls having different cod-end meshes was made by the author. The results indicate that small sized prawns of mean length 77.15 mm were captured by the net having 23.38 mm cod-end at 5-6 fathoms depth, medium prawns of mean length 105.22 mm was caught in 25.21 mm and 19.88 mm cod-end at 8 fathoms depth and big sized prawns of mean length 117.98 mm were caught in 21.29 mm cod-end. Further the relation of length on breadth of prawn is worked out to be : Bp=0.15 Lp - 1.50 where Bp and Lp are breadth and length respectively.

Studies on the possible sources of microbial contaminations of processed fishery products

An attempt has been made in the present study to estimate and describe in detail the nature and extent of contamination of processed fishery products. In large scale prawn processing when the preprocess preparation is elaborate, the industry in India has found it advantageous to establish the primary processing centers away from the processing factories. The data collected have clearly indicated that if such processing centers are not properly organized there is a possibility of greater contamination of the products at this stage. The data collected during the course of this investigation have given the basis for the measures to be taken for the maintenance of bacterial quality of prawn during different stages of processing.

Studies on technological problems associated with the processing of cooked frozen prawns. Pt. 1. Preprocess storage conditions of raw material in relation to quality

The chemical and organoleptic properties of prawn held in ice for different days prior to cooking and the changes after freezing and subsequent storage were studied with three different species of prawn viz. Metapenaeus monoceros, Metapenaeus dobsoni and Parapeneopsis stylifera. The optimum period for which the prawn can be kept under ideal conditions of icing prior to cooking has been worked out.

Studies on blackening of canned prawns. Pt. 1. Influence of copper and iron on product blackening

A linear relationship was observed between the copper content and intensity of blackening in commercially canned prawn meat. Average copper and iron contents of non-blackened canned prawn meat were 9.6 and 32.5 ppm on dry weight basis respectively. In the blackened product copper content ranged from 15.8 to 63.9 ppm and iron content between 43.7 and 71.45 ppm depending on the intensity of blackening. But incorporation of copper in the above range to experimental cans produced blackening while iron up to 250 ppm did not impart any blackening under standard conditions of canning.

Fish and shell fish fauna of the retting and nonretting zones of the Kadinamkulam kayal, Kerala

Retting of coconut husk is one of the major problems of pollution in the estuaries (kayals) of Kerala. Retting activity has resulted in the mass destruction of the flora and fauna and has converted sizeable sections of the kayal into virtual cesspools of foul smelling stagnant waters. Levels of hydrogen sulphide, phosphate and BOD, increased while dissolved oxygen and fish and shellfish fauna decreased in the ambient waters. In the Kadinamkulam kayal a total of 37 species of fishes belonging to 26 families, 5 species of prawn and 2 species each of crabs and molluscs were recorded from the no retting zone, whereas only 20 species of fish in dead condition were collected from the rating zone. Prawns, crabs and molluscs were absent at the vetting zone. Majority of the fish fauna in the kayal were marine forms.

Biodiversity in floodplains with special reference to artificial stocking

A five years investigation on fish biodiversity in connection with artificial stocking was conducted in three south-western floodplains of Bangladesh from 1992 to 1996. The ten top most available and ten rarest fish species were identified. Puntius sp., Channa punctatus, Mystus sp., Anabus testudinius, Ambasis sp., Colisha sp. and Macrobrachium sp. etc. were the most common available species. On the other hand, Mystus aor, Notopterus chitala, Clupisoma garua, Aplocheilus panchax, Ctenophmyngodon idella etc. were the rarest species. However, the most abundant and the rarest fish species behaved differently in different floodplains in different years. Shannon diversity index was used to assess the extent of diversity in different years. The study revealed that the artificial stocking programme, to some extent, influenced the biodiversity in floodplains.

Protein from blanch liquor

A process is described for isolation of edible protein from blanch liquor, which is discarded as a waste at present from prawn canning factories. The protein isolated is colourless and odourless and contains an appreciable amount of salt from the brine used for blanching prawns. It is comparable to fish protein concentrate in amino acid composition.